The subject matter disclosed herein relates generally to a rotor structure of an electric machine such as a generator. More particularly, the invention relates to an electric machine having a laminated rotor structure including chamfers on the laminations to reduce smearing.
Generators typically include a stator and a rotor, the rotor rotating about a longitudinal axis within the stator to convert mechanical energy into electrical energy. The stator typically includes windings from which electrical power is output.
The rotor includes radially cut slots about the circumference of the rotor body, which extend lengthwise along the rotor body. These slots contain the coils which form the rotor field windings for carrying current. The rotor field windings are supported in place against centrifugal forces by using one of a number of different systems including, e.g., coil wedges which bear against the slot surfaces. The regions of the coils which extend beyond the ends of the rotor body are referred to as end windings, and are supported against centrifugal forces by retaining rings. The portion of the rotor shaft forging which is located under the rotor end windings is referred to as the spindle.
Rotors may be formed from a solid single forging of high strength iron or steel, which provide the rotor with the required bending stiffness to support the rotor both statically and to transmit torque from the rotor to a drive flange of the generator for successful operation of a large, high speed generator. These solid single-forging rotors are expensive to produce, and limited production capacity may result in long lead times for ordering and manufacture.
Laminated rotor bodies have been used in some electric machines such as generators and motors to alleviate the expense and lead time associated with solid steel rotors. These laminated rotor bodies comprise laminations placed on, or attached to, a single steel shaft, such that the shaft provides the required bending stiffness for the rotor. Laminated rotor bodies have also been used in electric machines in which the stack of laminations is held in compression by a series of rods that pass through holes in the periphery of the laminations.
After assembly of a laminated rotor, surfaces that serve as mechanical load transfer interfaces typically need machining to avoid stress concentration, and likelihood of resultant failure. Additional machining may be needed to form and/or shape mating surfaces between the rotor and wedges which hold the windings in place. Further, the assembled rotor may have excessive radial runout, which may require machining of the outer diameter of the rotor body to reduce to an acceptable level. The machining that the rotor may undergo following assembly may result in smearing, or electrical contact between laminations, across insulation layers between laminations.